It's not difficult to reschedule an interview. Simply make an in-person meeting with Infopass and explain your reasoning to the officer. I wouldn't recommending calling to reschedule.
But unless you have a legitimate reason for missing the interview (my husband had 2 law school exams the day of our interview), I don't recommend doing it. Even the officer tried to talk me out of dong it until he heard the reason why.
Also, make sure you make the Infopass appt. as soon as humanly possible. The officer praised me for coming a month in advance of the original interview date and told me stories of people who tried unsuccessfully to reschedule 2 days before their interview.
Please note that rescheduling will delay your overall process. My original interview date was December 2, 2009. My rescheduled interview was 2 months later - on February 1, 2010.
